As olefin polymerization catalysts, so-called Kaminsky catalysts are well known. The catalysts have extremely high polymerization activity, so that polymers having a narrow molecular weight distribution can be obtained. As the transition metal compounds used for the Kaminsky catalysts, for example, bis(cyclopentadienyl) zirconium chloride (see, JP A 58(1983)-19309) or ethylenebis(4,5,6,7-tetrahydroindenyl) zirconium dichloride (see, JP A 61(1986)-130314) are known.
It is also known that olefin polymerization activity and obtained polyolefin properties differ vastly depending on the type of transition metal compounds used for polymerization.
Further, as a new olefin polymerization catalyst, a transition metal compound having a ligand chelate-coordinating with a hetero atom is recently proposed as described in JP A 11(1999)-199592.
Polyolefins generally have excellent mechanical properties, and hence have widely been employed in various fields such as molded products of all sorts. However, since the demands for physical properties of polyolefins have been diversified recently, polyolefins with various properties have increasingly been desired.
Further, in order to improve productivity, the increase of polyolefin yield per catalyst amount and the maintenance of catalytic activity are especially important subjects.
The present invention has been made in view of the above circumstances of the prior art. An object of the present invention is to provide a process for polymerizing an olefin with excellent polymerization activity using the transition metal compound proposed in JP A 11(1999)-199592.